Damping of subsynchronous resonance oscillations with TCSC and PSS and their control interaction

Typically the control systems of a thyristor-controlled series compensator (TCSC) employ a conventional type controller to obtain a reactance order. As the characteristic of a TCSC is non-linear in nature, this becomes necessary. The reactance order is then converted into the corresponding firing angle of the TCSC through a look-up table. The main drawback of this approach is the absence of a closed-loop model through which the stability of the system can be analyzed. To alleviate this problem a linear, discrete-time state space model of a TCSC compensated transmission line in the d- q domain is proposed in P.C. Srivastava, A. Ghosh, S.V. Jayaram Kumar, Model-based control design of a TCSC compensated power system, Electr. Power Energy Syst. (submitted for publication). In this paper we use this discrete-time model for studying the control interaction between a TCSC and a power system stabilizer (PSS) in damping torsional oscillations arising due to subsynchronous resonance (SSR). To do this, an overall system model in the linearized domain is developed first for eigenvalue analysis of the IEEE first benchmark model (IEEE-FBM) for SSR analysis IEEE SSR Task Force, “First benchmark model for computer simulation of subsynchronous resonance,” IEEE Trans. Power Appar. Syst., 96 (5) pp. 1565–1572 (1979). Through this eigenvalue analysis, the controller parameters are chosen, which are then used in PSCAD/EMTDC simulation studies.